On Mon, May 25, 2020 at 08:47:30AM -0700, Paul E. McKenney wrote:
> On Mon, May 25, 2020 at 01:25:21PM +0200, Peter Zijlstra wrote:
> > That is; how can you use a spinlock on the producer side at all?
>
> So even trylock is now forbidden in NMI handlers? If so, why?
The litmus tests don't have trylock.
But you made me look at the actual patch:
+static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size)
+{
+ unsigned long cons_pos, prod_pos, new_prod_pos, flags;
+ u32 len, pg_off;
+ struct bpf_ringbuf_hdr *hdr;
+
+ if (unlikely(size > RINGBUF_MAX_RECORD_SZ))
+ return NULL;
+
+ len = round_up(size + BPF_RINGBUF_HDR_SZ, 8);
+ cons_pos = smp_load_acquire(&rb->consumer_pos);
+
+ if (in_nmi()) {
+ if (!spin_trylock_irqsave(&rb->spinlock, flags))
+ return NULL;
+ } else {
+ spin_lock_irqsave(&rb->spinlock, flags);
+ }
And that is of course utter crap. That's like saying you don't care
about your NMI data.
